To further improve integration degrees of semiconductors such as of a large scale integration (LSI), it is desired to make finer patterns during productions of semiconductors, and currently the smallest pattern size is 100 nm or shorter.
Formations of such fine patterns in semiconductor devices have been realized by shortening wavelength of light from a light source of exposure devices and improving resist materials. Currently, formations of fine patterns have been performed by a liquid immersion lithography, in which exposure is performed through water with a light source that emits argon fluoride (ArF) excimer laser light having a wavelength of 193 nm, and as a resist material used for the lithography, various ArF resist materials, which use acrylic resins as a base, have been developed. Moreover, as a lithography technique of the next generation, extreme ultraviolet (EUV) lithography using as a light source, soft X rays having a wavelength of 13.5 nm has been studied, and therefore it is obvious that a pattern size will continue to be reduced, e.g. 30 nm or shorter, in the future.
Along with the above-mentioned reduction of the pattern size, unevenness of a resist pattern line width, i.e. line width roughness (LWR), of the resist pattern has become more significant, and this may adversely affect performances of a resulting device.
To solve the problems as mentioned, there are attempts to optimize exposure devices and resist materials for use. However, satisfactory results have not been obtained. Moreover, it takes a great deal of cost and time to improve exposure devices and resist materials.
Accordingly, various countermeasures have been studied and provided in terms of process conditions.
For example, the method of improving LWR is disclosed, and in this method, a resist pattern is treated with an aqueous solution containing an ionic surfactant in a rinsing process, which is performed after a developing process, so as to dissolve the roughness of the resist pattern at the same time as reducing defects (e.g. defects including residues, and deformation of the pattern) caused by the developing process (Japanese Patent Application Laid-Open (JP-A) No. 2007-213013).
Moreover, another method is disclosed in JP-A No. 2010-49247, and in this method an organic coating material, to which a low molecular acidic compound containing a carboxyl group, is applied to a resist pattern that has been developed, and the coating material is then removed to thereby improve LWR as well as sliming the resist pattern (see JP-A No. 2010-49247).
However, any of these methods has a problem that a desirable resist pattern size cannot be obtained as the improvement of LWR is realized by removing a surface of a resist pattern by processing. Moreover, these methods have a problem that LWR may be potentially worsened.
The present inventors have disclosed a resist pattern thickening material that enables precise processing by swelling (thickening) the resist pattern (Japanese Patent (JP-B) No. 3633595, and JP-A No. 2006-259692).
In the case where a resist pattern is subjected to a thickening process using such resist pattern thickening material, however, a size of the resist pattern is largely changed. Therefore, it is not suitable for a material for improving LWR, which desirably improves LWR of a resist pattern, without changing a size of the resist pattern more than necessary.
Accordingly, it is currently desired to provide a resist pattern improving material, a method for forming a resist pattern, and a method for producing a semiconductor device, that can improve LWR of a resist pattern without changing a size thereof more than necessary.